The Reduction of Cu II Compounds by Excimer Laser Irradiation for Copper Metal Deposition
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THE REDUCTION OF Cull COMPOUNDS BY EXCIMER LASER IRRADIATION FOR COPPER METAL DEPOSITION
M.SUYS, B.MOFFAT, M.-H.BERNIER, R.IZQUIERDO, S.POULIN, M.MEUNIER and E.SACHER
DUpartement de g6nie physique and Groupe des Couches Minces, Ecole Polytechnique de Montr6al, Montr6al, Qudbec, Canada, H3C 3A7.
ABSTRACT The short (UV) wavelength and the large beam cross-section of excimer lasers
are expected to permit high resolution projection patterning and, for this reason, excimer laser deposition of Cu from organometallic precursors appears to be an interesting alternative for metallization in ULSI circuits. Unfortunately, the photolytic decomposition of those precursors leads to strong carbon contamination of the deposits. However, the valence state of the Cu in such deposits is unknown. In this paper, the reduction of two Cu (11)compounds, Cu(hmac)2 and Cu(hfac)2, under excimer laser irradiation in a hydrogen ambient is discussed. It is shown, with X-ray Photoelectron Spectroscopy, that, under our experimental conditions, Cu(hmac)2 is reduced to a Cu (I) compound while some of the Cu(hfac) 2 appears to be reduced to the metallic state. Furthermore, reaction of the SiO 2 substrate with the carbon from the Cu(hmac)2 precursor is observed. INTRODUCTION
Copper is known to have a high electromigration resistance, low resistivity and high melting point compared to the commonly used materials for interconnections, Al and Al-Cu. However, since it diffuses rapidly in silicon [1], Cu is a good candidate material only for upper level metallization. To achieve this metallization, several groups have discussed the Chemical Vapor Deposition (CVD) of Cu, using a variety of Cu (I) and Cu (11)organometallic precursors [2-121 chosen for their volatility at moderate temperatures, thermal stability, ease of reduction to metallic Cu and volatile organic products, and low toxicity [13]. Given the difficulty in etching copper with submicronic resolution, selective processes are an attractive alternative. Laser CVD of Cu, using some of those same precursors, is such a selective process and has been reported by a few authors [14-25]. From those reports, it appears that a pyrolytic reduction of the precursors, using a visible laser beam, leads to pure Cu while a photolytic reduction, using a UV beam, leads to deposits strongly contaminated with carbon. However, the short wavelength of an excimer laser is advantageous in that it would permit large surface projection patterning of high resolution interconnections. To achieve the deposition of a pure metallic Cu film with an excimer laser, it is therefore essential to gain a better understanding of the reaction actually taking place and to determine the nature of the non-volatile carbon species contaminating the deposits. We present here results obtained from the study of the reduction of two Cu (11)precursors, Cu(hfac) 2 and Cu(hmac) 2, under KrF excimer laser irradiation at 248 nm using hydrogen as both the carrier and the reductant gas.
Mat. Res. Soc. Symp. Proc. Vol. 282. ©1993 Materials Resea
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